kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

5 files changed, 103 insertions, 0 deletions

diff --git a/arch/mips/mobileye/Kconfig b/arch/mips/mobileye/Kconfig
new file mode 100644
index 000000000..8a4868d2e
--- /dev/null
+++ b/arch/mips/mobileye/Kconfig
@@ -0,0 +1,29 @@
+# SPDX-License-Identifier: GPL-2.0
+if EYEQ
+
+choice
+	prompt "Mobileye EyeQ SoC selection"
+	default MACH_EYEQ5
+	help
+	  Select Mobileye EyeQ MIPS SoC type.
+
+	config MACH_EYEQ5
+		bool "Mobileye EyeQ5 SoC"
+
+	config MACH_EYEQ6H
+		bool "Mobileye EyeQ6H SoC"
+
+	config MACH_EYEQ6LPLUS
+		bool "Mobileye EyeQ6Lplus SoC"
+endchoice
+
+config FIT_IMAGE_FDT_EPM5
+	bool "Include FDT for Mobileye EyeQ5 development platforms"
+	depends on MACH_EYEQ5
+	default n
+	help
+	  Enable this to include the FDT for the EyeQ5 development platforms
+	  from Mobileye in the FIT kernel image.
+	  This requires u-boot on the platform.
+
+endif
diff --git a/arch/mips/mobileye/Makefile b/arch/mips/mobileye/Makefile
new file mode 100644
index 000000000..315c06b68
--- /dev/null
+++ b/arch/mips/mobileye/Makefile
@@ -0,0 +1 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
diff --git a/arch/mips/mobileye/Platform b/arch/mips/mobileye/Platform
new file mode 100644
index 000000000..93b533492
--- /dev/null
+++ b/arch/mips/mobileye/Platform
@@ -0,0 +1,17 @@
+#
+# Copyright (C) 2016 Imagination Technologies
+# Author: Paul Burton <paul.burton@mips.com>
+#
+# This program is free software; you can redistribute it and/or modify it
+# under the terms of the GNU General Public License as published by the
+# Free Software Foundation;  either version 2 of the  License, or (at your
+# option) any later version.
+#
+
+load-$(CONFIG_MACH_EYEQ5)	= 0xa800000808000000
+load-$(CONFIG_MACH_EYEQ6H)	= 0xa800000100800000
+load-$(CONFIG_MACH_EYEQ6LPLUS)	= 0xa800000108800000
+all-$(CONFIG_MACH_EYEQ5)	+= vmlinux.gz.itb
+
+its-y					:= vmlinux.its.S
+its-$(CONFIG_FIT_IMAGE_FDT_EPM5)	+= board-epm5.its.S
diff --git a/arch/mips/mobileye/board-epm5.its.S b/arch/mips/mobileye/board-epm5.its.S
new file mode 100644
index 000000000..08e8c4f18
--- /dev/null
+++ b/arch/mips/mobileye/board-epm5.its.S
@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: (GPL-2.0 OR MIT) */
+/ {
+	images {
+		fdt-mobileye-epm5 {
+			description = "Mobileeye MP5 Device Tree";
+			data = /incbin/("boot/dts/mobileye/eyeq5-epm5.dtb");
+			type = "flat_dt";
+			arch = "mips";
+			compression = "none";
+			hash {
+				algo = "sha1";
+			};
+		};
+	};
+
+    configurations {
+		default = "conf-1";
+		conf-1 {
+			description = "Mobileye EPM5 Linux kernel";
+			kernel = "kernel";
+			fdt = "fdt-mobileye-epm5";
+		};
+	};
+};
diff --git a/arch/mips/mobileye/vmlinux.its.S b/arch/mips/mobileye/vmlinux.its.S
new file mode 100644
index 000000000..3e2546765
--- /dev/null
+++ b/arch/mips/mobileye/vmlinux.its.S
@@ -0,0 +1,32 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/dts-v1/;
+
+/ {
+	description = KERNEL_NAME;
+	#address-cells = <ADDR_CELLS>;
+
+	images {
+		kernel {
+			description = KERNEL_NAME;
+			data = /incbin/(VMLINUX_BINARY);
+			type = "kernel";
+			arch = "mips";
+			os = "linux";
+			compression = VMLINUX_COMPRESSION;
+			load = /bits/ ADDR_BITS <VMLINUX_LOAD_ADDRESS>;
+			entry = /bits/ ADDR_BITS <VMLINUX_ENTRY_ADDRESS>;
+			hash {
+				algo = "sha1";
+			};
+		};
+	};
+
+	configurations {
+		default = "conf-default";
+
+		conf-default {
+			description = "Generic Linux kernel";
+			kernel = "kernel";
+		};
+	};
+};